1. Field of the Invention
The present invention relates to a technology for scanning a target surface with a light beam.
2. Description of the Related Art
In recent years, there has been a growing demand for low-cost image forming apparatuses such as laser printers and digital copiers. One approach for achieving such low-cost image forming apparatuses is to employ scanning lenses made of plastic in an optical scanning device. However, because plastic exhibits a greater change in optical characteristics due to moisture absorption or temperature change than glass, there is a risk of changing the diameter of a light spot on the surface to be scanned from a change in the operating environment.
To overcome this problem, optical scanning devices that reduce the amount of change in spot size resulting from fluctuation in environmental factors, such as temperature and humidity, while still employing a plastic optical element have been proposed (see, for example, Japanese Patent No. 3483141, Japanese Patent No. 3483129, and Japanese Patent Application Laid-open No. 2002-277783).
Unfortunately, the optical scanning devices disclosed in the above literatures require a plurality of lenses to be positioned with high accuracy or need to employ many components in addition to lenses. Therefore, it is expected that enhancing the scanning accuracy at low cost will be difficult using these optical scanning devices.